In tandem mass spectrometry, ions formed in a source are mass analyzed by means of an analyzing element, such as a magnet sector, quadrupole or hybrid system. Ions of a selected mass are then introduced into a region of the spectrometer in which a relatively high pressure of a selected gas in present. These ions then interact with the gas atoms or molecule in such a way that the internal energy of the ion is increased to the point where fragmentation of the ion occurs. The resulting fragments, in particular those having an ionic charge, are further mass analyzed and identified.
Tandem Mass Spectrometry has been described by (a) F.W. McLafferty, Ed., "Tandem Mass Spectrometry", John Wiley and Sons, Inc., 1983; (b) R.G. Cooks, in "Collision Spectroscopy", R.G. Cooks, Ed., Plenum Press, 1978, p.357; (c) R.W. Kondrat and R.G. Cooks, Anal. Chem., 50 (1978), A81; (d)F.W. Crow, K.B. Tomer, and M.L. Gross, Mass Spectrom. Rev., 2 (1983), 47. In U.S. Pat. Nos. 4,234,791, 4,328,420 and 4,329,582 there is disclosed a tandem quadrupole-based mass spectrometer including a highly efficient intermediate fragmentation stage. The disclosed fragmentation stage employs collision-induced dissociation (CID), in an electrodynamic focus device, which may be a quadrupole operated as a broad band filter mode. This process of fragmentation (CID) is a controlled process compared with ionization processes which occur in traditional mass spectrometry sources. As a result, the types of fragmentations which occur can be more readily interpreted in terms of the structures of the intact species. This feature, and the advantages of two stages of mass analysis in improving selectivity of detection, has resulted in MS/MS being widely used in qualitative and quantitative molecular analysis, in ion structural studies, and in gas phase ion chemical investigations. Larger molecules, in particular, resist fragmentation in CID because the energy supplied is rapidly distributed among the many internal degrees of freedom of the species. Larger energies are needed to overcome this problem. This is of particular significance in the application of mass spectrometry to the biological sciences.
Dissociation of molecules on collision at surfaces has been reported by R.G. Cooks, T. Ast, and J.H. Beynon, Int. J. Mass Spectrom. Ion Phys., pg.348, 16 (1975), among others. The interactions of polyatomic ions with surfaces have been shown to be a source of information on the nature of the ionic species as well as the properties of the surface, M.A. Mabud, M.J. DeKrey and R.G. Cooks, Int. J. Mass Spectrom Ion Physics, 67, 285 (1985). Processes which occur include charge transfer, ion/surface reactive collisions, sputtering, reflection (elastic collisions) and inelastic collisions leading to dissociation of the emerging ion, M.S. Mabud, M.J. DeKrey, R.G. Cooks and T. Ast, Int. J. Mass Spectrom Ion Proc., 69, 277 (1986). This last process offers the possibility of supplementing or replacing gas phase collisions in tandem mass spectrometry (MS/MS). A tandem spectrometer has been constructed using a magnetic sector and a quadrupole mass filter arranged so that the angle made between the direction of motion of the ion emerging from the first mass analyzer and the direction of motion of that entering the second analyzer was large, 90.degree., M.J. DeKrey, M.A. Mabud, R.G. Cooks and J.E.P. Syka, Int. J. Mass Spectrum Ion Proc., 67, 295 (1985) and 77, 31 (1987).